The present invention relates to a bidirectional MOSFET switching circuit operating with a single gate bias, and more particularly to such a circuit including a pair of common-drain-connected power MOSFETs of the source-to-base-shorted type.
Bidirectional switching capability has been conventionally provided in circuits employing a pair of power MOSFETs with their sources connected in common and with their drains respectively connected to a pair of nodes for serial connection to a supply-and-load circuit. One such circuit is disclosed in U.S. Pat. No. 4,721,986, which is by the present inventor and assigned to the present assignee. Since the gate-to-source voltage of a power MOSFET typically determines its conduction state, the use of common-source-connected MOSFETs conveniently permits a single gate bias to simultaneously turn on both MOSFETs due to the common source connection.
It would, however, be desirable to provide a bidirectional MOSFET switching circuit employing a pair of common-drain-connected power MOSFETs, since common-drain-connected MOSFETs allow more efficient vertical current conduction in a monolithic IC using available technology. It would further be desirable to provide such a switching circuit with a single gate bias voltage for turning on both power MOSFETs despite the lack of a common source connection for providing common gate-to-source biasing.
The foregoing problem is overcome in one form of the invention which, as briefly stated, includes the combination of (i) a bidirectional switching circuit including a pair of common-drain-connected power MOSFETs having their sources respectively connected to a pair of nodes for serial connection to a load-and-supply circuit and (ii) a gate control circuit for providing gate bias for both power MOSFETs from a single gate bias voltage respectively provided between first and second nodes. The power MOSFETs are of the source-to-base-shorted type so that each contains an inherent P-N diode. The gate control circuit, in preferred form, comprises a pair of common-source-connected gate control MOSFETs with their sources commonly connected to the first node; with their drains respectively connected to the respective gates of the pair of power MOSFETs; and with their gates connected in common to the second node and to the common-connected drains of the power MOSFETs.
In operation of the invention, the inherent P-N diode of the second-to-turn-on power MOSFET approriately biases the source of such second-to-turn-on transistor to induce such transistor to turn on.
Other objects and features of the present invention will become apparent from the following description of the preferred embodiments of the invention considered in conjunction with the accompanying drawings.